A conventional hand-held electric caulking gun disclosed in U.S. Pat. No. 4,171,072 comprises a caulk-driving piston forced through the caulk-retaining receptacle of the gun. The gun includes a clutch for drivably disengaging the drive source from the piston and a releasing device for allowing the piston to be disengaged from its driving linkage with a motor.
A conventional quick release for helically-threaded drive unit disclosed in U.S. Pat. No. 4,322,022 is provided with a quick release feature. As the release feature is activated, the active portions of the drive nut of a lead screw in the drive train are disconnected from the lead screw, allowing the internal pressure in the chamber of the cartridge to be quickly equilibrated by pushing the piston and its lead screw backwards. Then, the dispensing can be stopped and sharply curtailed, merely by releasing the trigger on the power hand tool and activating the quick release.
A conventional apparatus for mixing and dispersing multiple-component substances disclosed in U.S. Pat. No. 5,286,105 comprises two cartridges with pistons and advanced in common by an electrical motor via a magnetic clutch. When switching off the motor and disengaging the clutch, the pistons are manually retracted and re-advanced. Then the pistons entrain a shaft which serves to drive a mixer head. The cartridge connecting with the mixer head can be removed as a unit from the apparatus and replaced by another unit for exchanging the emptied cartridges.
The conventional apparatus for mixing and delivering multi-component substances, particularly for expressing said mixed substances onto a tray during the taking of a dental impression, comprises a housing, an electronic button mounted on the housing, driving gears, two gear racks, a dual-barrel cartridge, and a mixer head. The driving gears, the two gear racks, the dual-barrel cartridge, and the mixer head are positioned in the housing. The driving gears trigger motion of the two gear racks, and the two gear racks are each respectively connected to each of the two chambers of the cartridge, pushing the two component substances contained in each of the chambers into the mixer head. As a user pushes the electronic button, each of the two gear racks will be pushed equally and in synchrony into each of the two chambers of the cartridge resulting in the different component substances contained in each of the chambers being pushed into the mixer head; in the meantime, the build-up of viscoelastic pressure inside the cartridge will cause a slight expansion of its walls. Therefore, as the user stops pushing the electronic button, the relaxation of the viscoelastic pressure will allow relaxation of the cartridge walls, resulting in an undesirable oozing and waste of the component substances.
Besides, as the cartridge is emptied and the user wants to replace it with a full one, due to the manner by which the pistons and gears are positioned in the cartridge, the user has to press and hold a reverse button in order to allow the gears to rotate in reverse, which causes the pistons to disengage from the cartridge. Thus, it is rather time consuming to change the cartridge.
Furthermore, the desktop conventional apparatus for mixing different component substances of the silicone-based dental impression material is heavy and not easy to move. Therefore, being non-portable, each treatment room is required to have its own heavy, bulky, and expensive machine.